A storage battery for household or industrial use has an issue that the battery, when fully charged, has a reduced capacity due to repeated charges and discharges (charge-discharge). For this reason, techniques for estimating a full capacity of a storage battery are conventionally used (see PTL 1 and PTL 2, for example).
According to the method for computing a remaining capacity of a storage battery described in PTL 1, the storage battery is discharged until the voltage reaches a discharge alarm voltage. Then, according to the method described in PTL 1, the storage battery is charged until fully charged. Then, according to the method described in PTL 1, as a replenishing charge capacity, a charge capacity from a state in which the voltage of the storage battery has dropped to the discharge alarm voltage to fully charged is computed. Then, according to the method described in PTL 1, as a new learned capacity of the storage battery, a value is computed by adding the replenishing charge capacity to a discharge alarm capacity, which is the battery capacity remaining when the battery is discharged up to the discharge alarm voltage.
According to the method described in PTL 1, a new learned capacity of the battery is computed by adding the replenishing charge capacity to the discharge alarm capacity, which is the remaining amount in the storage battery at the end of discharging. Thus, the method described in PTL 1 can calculate the learned capacity even in the degraded storage battery. In addition, according to the method described in PTL 1, the remaining amount in the storage battery is computed by subtracting the discharge capacity from the charge capacity of the storage battery, and then the remaining capacity (SOC (state of charge)) is computed based on the ratio between the computed remaining amount and the learned capacity. Thus, the method described in PTL 1 achieves correct computation of, in particular, the remaining capacity at the end of discharging.
According to the method for detecting a full-charge capacity of a storage battery described in PTL 2, a first no-load voltage (VOCV1) of the storage battery as of a first no-load timing when the storage battery is in the no-load state and a second no-load voltage (VOCV) of the storage battery as of a second no-load timing are detected. Then, according to the method described in PTL 2, it is determined whether the detected first no-load voltage (VOCV1) falls within a predetermined voltage range. According to the method described in PTL 2, when the first no-load voltage (VOCV1) falls within the predetermined voltage range, a first remaining capacity (SOC1 [%]) of the storage battery is determined from the detected first no-load voltage (VOCV1). Then, according to the method described in PTL 2, a second remaining capacity (SOC2 [%]) of the storage battery is determined from the second no-load voltage (VOCV2). Next, according to the method described in PTL 2, the rate of change (δS [%]) in remaining capacity (SOC [%]) is computed based on a difference between the first remaining capacity (SOC1 [%]) and the second remaining capacity (SOC2 [%]). In addition, according to the method described in PTL 2, the change in capacity value (δAh) of the storage battery is computed based on an integrated value of the charge current and discharge current of the storage battery to be charged-discharged between the first no-load timing and the second no-load timing. Then, according to the method described in PTL 2, the full-charge capacity (Ahf) of the storage battery is computed by applying the rate of change (δS [%]) in remaining capacity (SOC [%]) and the change in capacity value (δAh) to the equation: “Ahf=δAh/(δS/100)”.
According to the method described in PTL 2, first and second remaining capacities are determined based on first and second no-load voltages as of first and second no-load timings. Then, according to the method described in PTL 2, the change in capacity value of the storage battery is computed based on an integrated value of the charge current and discharge current of the storage battery being charged-discharged between the first and second no-load timings. Then, according to the method described in PTL 2, the full-charge capacity of the storage battery is computed based on the rate of change in remaining capacity and the change in capacity value between the first and second no-load timings. Accordingly, the method described in PTL 2 can compute a full-charge capacity of a storage battery without using full charge after the storage battery is completely discharged.